In recent years, wireless power transmission systems are put to practical use for wirelessly transmitting electric power to electronic devices such as smartphones, tablet terminals, and the like. For example, Patent Documents 1 to 3 describe such wireless power transmission systems.
Patent Document 1 discloses an electromagnetic induction type wireless power transmission system. The electromagnetic induction type wireless power transmission system includes a wireless power transmitter device and a wireless power receiver device. The wireless power transmitter device includes a power transmitter coil, and the wireless power receiver device includes a power receiver coil. Electric power is transmitted between these coils.
Patent Document 2 discloses an electromagnetic induction type wireless power receiver device.
Patent Document 3 discloses a capacitive coupling type wireless power transmission system. The capacitive coupling type wireless power transmission system includes a wireless power transmitter device and a wireless power receiver device. The wireless power transmitter device includes a power transmitter electrode, and the wireless power receiver device includes a power receiver electrode. Electric power is transmitted between these electrodes via electrostatic induction.
Patent Document 1: Japanese Patent No. 3344593
Patent Document 2: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2006-510101
Patent Document 3: International Publication No. 2011/148803
There is a need for wireless power transmission in conventional electronic devices such as smartphones, tablet terminals, and the like, which have no wireless power transmission capability. It is considered that one way of satisfying the need is to attach an external wireless power receiver device to the foregoing electronic device. Here, these electronic devices are being downsized and made thinner to improve user-friendliness. Thus, even for such an external wireless power receiver device, it is desirable to have a smaller and thinner shape.